Improve Error Messaging for Error Responses #5970

Currently, KoboToolbox responds with a generic HTTP 500 Internal Server Error in several scenarios, including but not limited to:

• When required information is missing or malformed in the request
• When a file size limit is exceeded
• When there is any kind of conflict during submission or processing

In all these cases, the 500 error is returned without a descriptive message indicating the cause of the error.

Why this matters:

This behavior makes it difficult for users and developers to understand what went wrong and how to correct it. It also hinders the ability to provide accurate bug reports or support requests, as there is no visibility into the underlying issue.

Suggested improvement:

For every 500 error (and ideally for all 4xx and 5xx errors), KoboToolbox should return a descriptive error message in the response body. This message should clearly indicate the reason for the failure, such as:

• "File size exceeds the allowed limit of X MB."
• "Missing required parameter: submission.xml."
• "Conflict: Submission with this ID already exists."

Expected benefits:

• Improves user experience and reduces frustration
• Helps users and developers correct submission issues more efficiently
• Leads to more useful and specific bug reports, improving the development feedback loop
• Aligns with best practices for API error handling

We hope this can be prioritized as part of ongoing usability and developer experience improvements.